License Validation: Customer Token 1.0.0

This add-on extends [XI] License Validation by adding an additional condition which ensures that a customer token is not assigned to more than one account. So this will make it much more difficult to have (validated) dupe accounts. Note that there will be a new column in xf_user that stores the customer tokens.

There are also six new phrases prefixed with awedo_lvct_. The phrases that are postfixed with _log are the messages for the server error log and those postfixed with _show are shown to the user.